PET devices in which coincidence radiation detectors for detecting lines of response of annihilation radiations are arranged in a ring shape around a field of view (see Japanese Patent Application Laid-Open No. 2007-71858 (hereinafter, Patent Literature 1) and Japanese Patent No. 5339561 (hereinafter, Patent Literature 2)) have been widely known.
PET needs to obtain lines of response (LORs) at various angles (projection angles). In PET, radiation detectors are therefore arranged in a shape of ring to surround a measurement target.
On the other hand, partially opened ring (referred to as “partial-ring”) PET devices with a part of the radiation detectors normally arranged in a ring shape for detecting line of response are removed have been developed in P. Crespo et al., “On the detector arrangement for in-beam PET for hadron therapy monitoring,” Phys. Med. Biol., vol. 51 (2006), pp. 2143-2163 (PET Imaging of Irradiation Field for Particle-Beam Cancer Therapy) (hereinafter, Non-Patent Literature 1) and Jun'ichi Oi et al., “Development of a ‘Flexible PET’ System Having Multi-Modality Compatibility,” Shimadzu Review, vol. 72, Nos. 3 and 4, (2016.3), pp. 65-71 (Multi-Purpose PET) (hereinafter, Non-Patent Literature 2). FIG. 1 shows an example of an opposed gamma camera type partial-ring PET device developed by the GSI Helmholtz Centre for Heavy Ion Research in Germany. In the diagram, the reference numeral 10 represents a field of view, the reference numeral 12 lines of response, and the reference numeral 14 coincidence radiation detectors (referred to as coincidence detectors) for detecting the lines of response 12.
A hybrid PET/MRI device in which a PET device and an MRI device are integrated to obtain both a PET image and an MRI image has also been developed (see Japanese Patent No. 5713468 (hereinafter, Patent Literature 3)). Like Non-Patent Literature 2, a PET device to be arranged and used in the bore of an MRI device (referred to as an MRI bore) without a change to the existing MRI device is also under development.
If the bed and radio frequency (RF) coil of an existing MRI device are used, there is room to arrange radiation detectors over a measurement target but no space to arrange radiation detectors under the measurement target. If the radiation detectors are arranged in a ring shape between the bed and the RF coil of the existing MRI device, the center position of the measurement target deviates from the center of the MRI bore. Such a configuration is not desirable for MRI imaging.